The present invention relates to a resin composition, and more particularly to a resin composition exhibiting a good adhesion when a surface of the resin composition is subjected to a wet processing for forming a conductor on a surface of the molded resin composition.
A plating process has been developed for the purpose of preventing static electricity on the surface of a molded resin composition. This plating process is also made for forming a patterned conductor on a predetermined part of the molded resin composition surface, typically forming a printed wiring board. Such plating processes may be isolated into two processes. The first one is a dry process using thin film technologies of such as evaporation and sputtering. The second one is a wet process, wherein a catalyst core is adsorbed on the resin composition surface, and of the resin composition is subsequently immersed into an electroless plating bath for precipitation of electroless plating. If the dry process is used, then the maximum thickness of the conducive film is only a few micrometers, namely it is difficult to form a thin conductive film. This means that the thick conductive film is formed in the wiring board, then the impedance of the wiring is high, namely it is difficult to reduce the impedance of the conductive film wiring on the wiring board. On the other hand, the dry process allows a good adhesion of conductor with the resin composition. However, the dry process is inferior in the productivity and cost performance, for which reason the dry process is not suitable for mass production at low cost.
Namely, the wet process is superior in cost performance but inferior in adhesion between resin composition and conductor. In order to improve the adhesion between resin composition and conductor, it is required to provide a roughness to the surface of the resin composition. Available methods for providing the roughness to the resin composition surface would be isolated into two typical ones. The first one is the mechanical and physical method. The second one is the chemical method using wet etching by chemical etchants. The mechanical and physical method is somewhat inferior in uniformity of roughness and adhesion to the fine patterns is not uniform. It is also difficult to obtain a sufficiently high adhesion with a hard resin. On the other hand, the chemical method is ineffective with chemical-resistant resins.
Some typical electroless plating processes for resin surface will be described.
Example 1: Co-polymerization of Resin Matrix with Components to be Corroded by Chemicals
The following description will be made in the case of acrylonitrile-butadiene-styrene resin (ABS resin). This resin has an island structure wherein the rubber component of butadiene is dispersed in the form of spherical particles in a body of acrylonitrile-butadiene (AB). If this resin is immersed in an oxidizing etchant, then the rubber component in the form of spherical particles positioned in the vicinity of surfaces of the body is selectively oxidized and dissolved into the etchant, whereby the surface of the resin is made rough. The plated film of conductor is securely engaged with the rough surface of the resin by the anchor effect.
It is known in the art to make the adhesive layer rough. In Japanese patent publication Nos. 63-10752 and Japanese laid-open patent publication No. 3-18096, it is disclosed that the rubber component of the acrylonitrile-butadiene-styrene rubbers is introduced into the adhesive of epoxy resins to obtain the same effect as described above.
Chromatic acid is used as an oxidizing etchant for selective etching of the rubber component dispersed in the form of spherical particles. The use of chromatic acid as the oxidizing etchant is not preferable in the light of recently required reduction of environmental pollution. Blending rubber component reduces heat resistivity, stability in size, and insulation performance or anti-migration performance.
Example 2: Blending Resin Matrix with Inorganic Insulator to be Dissolved into Chemicals
In Japanese laid-open patent publication No. 60-167492, it is disclosed that an inorganic insulator is used to be selectively etched by chemicals. Glass, magnesium oxide and calcium carbonate are, for example, available to obtain a desired adhesion.
Since such inorganic insulators, however, include alkali metals or alkali earth metals, there is raised a problem with deterioration in moisture resistance of the resin. For this reason, it is preferable to not include a large amount of such inorganic insulators into the resin. Further, generally, the inorganic insulator has a larger specific gravity than resins. Particularly if liquid inorganic insulators such as varnish is used, then the inorganic insulator is non-uniformly present in the resin matrix, and the probability of the inorganic insulator existing in the vicinity of the surface of the resin matrix is lower.
In the above circumstances, it was required to develop a novel resin composition free from the above problems and a novel method of forming a conductor on a surface of the resin component.